Method for controlling of valve timing of continuous variable valve duration engine

ABSTRACT

A method for controlling intake and exhaust valves of an engine includes: controlling, by an intake continuous variable valve timing (CVVT) device and an exhaust CVVT device, opening and closing timings of the intake valve and exhaust valves; determining, by a controller, a target opening duration of the intake and exhaust valves based on an engine load and an engine speed; modifying, by an intake continuous variable valve duration (CVVD) device and by an exhaust two-stage variable valve duration device, current opening and closing timings of the intake valve and exhaust valve based on the target opening durations. In particular, the exhaust two-stage VVD device switches a current opening duration of the exhaust valve to a first exhaust opening duration or a second exhaust opening duration which is shorter than the first opening duration based on the target opening duration of the exhaust valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 15/258,043, filed on Sep. 7, 2016, and claims priority to and the benefit of Korean Patent Application Nos. 10-2015-0176786, filed on Dec. 11, 2015, and 10-2017-0154705, filed on Nov. 20, 2017, the entirety of each of which are incorporated herein by reference.

FIELD

The present disclosure relates to a system and a method for controlling valve timing of a continuous variable valve duration engine.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

An internal combustion engine combusts mixed gas in which fuel and air are mixed at a predetermined ratio through a set ignition mode to generate power by using explosion pressure.

Generally, a camshaft is driven by a timing belt connected with a crankshaft that converts linear motion of a cylinder by the explosion pressure into rotating motion to actuate an intake valve and an exhaust valve, and while the intake valve is opened, air is suctioned into a combustion chamber, and while an exhaust valve is opened, gas which is combusted in the combustion chamber is exhausted.

To improve the operations of the intake valve and the exhaust valve and thereby improve engine performance, a valve lift and a valve opening/closing time (timing) may be controlled according to a rotational speed or load of an engine. Therefore, a continuous variable valve duration (CVVD) device controlling the opening duration of an intake valve and an exhaust valve of the engine and a continuous variable valve timing (CVVT) device controlling the opening and closing timing of the intake valve and the exhaust valve of the engine have been developed.

The CVVD device may control opening duration of the valve. In addition, the CVVT device may advance or retard the opening or closing timing of the valve in a state that the opening duration of the valve is fixed. That is, if the opening timing of the valve is determined, the closing timing is automatically determined according to the opening duration of the valve.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.

SUMMARY

The present disclosure provides a system and a method for controlling valve timing of a continuous variable valve duration engine that simultaneously controls duration and timing of the valve being equipped with a continuous variable valve duration device and a continuous variable valve timing device disposed on an intake valve side, and being equipped with a two-stage variable valve duration device and continuous variable valve timing device disposed on an exhaust valve side of a turbo engine vehicle.

In one form, a method for controlling intake and exhaust valves of an engine includes: controlling, by an intake continuous variable valve timing (CVVT) device, opening and closing timings of the intake valve; controlling, by an exhaust CVVT device, opening and closing timing of the exhaust valve; determining, by a controller, a target opening duration of the intake valve, a target opening duration of the exhaust valve, and at least one of a target opening timing or a target closing timing of the intake valve and the exhaust valve, based on an engine load and an engine speed; modifying, by an intake continuous variable valve duration (CVVD) device, current opening and closing timings of the intake valve based on the target opening duration of the intake valve; modifying, by an exhaust two-stage variable valve duration (VVD) device, current opening and closing timings of the exhaust valve based on the target opening duration of the exhaust valve; advancing, by the intake CVVD device, the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve by a predetermined value, or retarding the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve by a predetermined value, based on the target opening duration of the intake valve; and switching, by the exhaust two-stage VVD device, a current opening duration of the exhaust valve to a first exhaust opening duration or a second exhaust opening duration which is shorter than the first opening duration, based on the target opening duration of the exhaust valve.

The intake CVVD device advances the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve when the target opening duration of the intake valve is longer than a duration between the current opening timing and current closing timing of the intake valve.

In another form, the intake CVVD device retards the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve when the target opening duration of the intake valve is shorter than a duration between the current opening timing and current closing timing of the intake valve.

The method may further includes the step of adjusting, by the intake CVVT device, the current opening and closing timings of the intake valve to the target opening and closing timings of the intake valve, respectively.

In one form, the method may further have the step of adjusting, by the exhaust CVVT device, the current opening and closing timings of the exhaust valve to the target opening and closing timings of the exhaust valve, respectively.

During the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to a first intake opening duration in a first control region where the engine load is between first and second predetermined loads, and the controller controls the intake CVVD device to adjust a current intake opening duration to the first intake opening duration, and wherein the exhaust two-stage VVD device applies the first exhaust opening duration to the exhaust valve so as to control a valve overlap between the exhaust valve and the intake valve in the first control region.

The method further includes the step of fixing the opening and closing timings of the intake valve and the opening timing of the exhaust valve, and setting up the closing timing of the exhaust valve at a maximum value within sustainable combustion stability in the first control region.

In another form, during the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to the first intake opening duration in a second control region where the engine load is greater than the second predetermined load and equal to or less than a third predetermined load, and the controller controls the intake CVVD device to adjust a current intake opening duration to the first intake opening duration and the exhaust two-stage VVD device to apply the first exhaust opening duration to the exhaust valve.

In particular, the exhaust CVVT device retards the closing timing of the exhaust valve as the engine load is increased so as to increase the valve overlap, and after when the engine load is greater than or equal to a predetermined load, the exhaust CVVT device advances the closing timing of the exhaust valve to decrease the valve overlap in the second control region.

The method further includes the step of determining, by the controller, a third control region where the engine load is greater than a third predetermined load and less than a fourth predetermined load and the engine speed is between first and second predetermined speeds, or where the engine load is greater than the third predetermined load and equal to or less than a fifth predetermined load and the engine speed is between the second predetermined speed and a third predetermined speed; and applying, by the two-stage VVD device, the first exhaust opening duration to the exhaust valve, and advancing, by the intake CVVT device, the closing timing of the intake valve in the third control region.

In the third control region, the intake CVVT device advances the closing timing of the intake valve to be approximately at a bottom dead center when the engine speed is less than a predetermined speed, the intake CVVT device advances the closing timing of the intake valve to an angle after the bottom dead center when the engine speed is greater than or equal to the predetermined speed.

The method further includes the step of determining a fourth control region, by the controller, where the engine load is greater than a fourth predetermined load and equal to or less than a fifth predetermined load and the engine speed is equal to or greater than a first predetermined speed and equal to or less than a second predetermined speed; and applying, by the two-stage VVD device, the second exhaust opening duration to the exhaust valve, and controlling, by the intake CVVT device, the closing timing of the intake valve to be approximately at a bottom dead center in the fourth control region.

In the fourth control region, the controller controls the opening timing of the intake valve via the intake CVVT device and the closing timing of the exhaust valve to approach at a top dead center so as to reduce a valve overlap.

The method further includes the step of determining, by the controller, a fifth control region where the engine load is greater than a fifth predetermined load and equal to or less than a maximum engine load and the engine speed is between first and second predetermined speeds, and controlling, by the controller, a wide open throttle valve (WOT) and applying the second exhaust opening duration to the exhaust valve in the fifth control region such that an fresh air introduced into a cylinder evacuates a combustion gas from the cylinder.

In the fifth control region, the intake CVVT device advances the opening timing of the intake valve to be before a top dead center to generate the scavenging and controls the closing timing of the intake valve to be after the bottom dead center.

In addition, in the fifth control region, the controller retards the opening timing of the exhaust valve to be after a bottom dead center so as to reduce interference of exhaust and controls the closing timing of the exhaust valve to be after a top dead center to maintain a catalyst temperature.

The method further includes the step of determining, by the controller, a sixth control region where the engine load is greater than a fifth predetermined load and equal to or less than a maximum engine load and the engine speed is greater than a second predetermined speed and equal to or less than a third predetermined speed; and controlling a wide open throttle valve (WOT) by the controller, controlling the closing timing of the intake valve by the intake CVVT device, and applying the first exhaust opening duration to the exhaust valve by the two-stage VVD device, in the sixth control region, so as to reduce a knocking in the sixth control region.

In the sixth control region, the controller advances the opening timing of the exhaust valve to be before a bottom dead center to inhibit an exhaust pumping and to lower boost pressure, and the controller controls the closing timing of the exhaust valve to be approximately at a top dead center.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, references being made to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing a system for controlling valve timing of a continuous variable valve duration engine according to one form of the present disclosure;

FIG. 2 is a perspective view showing a continuous variable valve duration device and a continuous variable valve timing device which are disposed on an intake valve side, and a two-stage variable valve duration device and continuous variable valve timing device which are disposed on an exhaust valve side;

FIG. 3 is a side view of an intake continuous variable valve duration device assembled with an intake continuous variable valve timing device which is disposed on an intake valve side;

FIG. 4 is a partial view of an inner wheel and a cam unit of an intake continuous variable valve duration device in one form;

FIGS. 5A-5C are views illustrating the operation of an intake continuous variable valve duration device in FIG. 4;

FIGS. 6A and 6B are views illustrating a cam slot of an intake continuous variable valve duration device in exemplary forms;

FIGS. 7A-7C are valve profiles of an intake continuous variable valve duration device in one form;

FIGS. 8A-8D illustrate a change of an opening duration and opening and closing timings of a valve;

FIGS. 9A and 9B are flowcharts showing a method for controlling valve timing of a continuous variable valve duration engine according to one form of the present disclosure;

FIG. 10 is a schematic diagram illustrating control regions in one form;

FIGS. 11A-11C are graphs showing duration, opening timing, and closing timing of an intake valve depending on an engine load and an engine speed in one form of the present disclosure; and

FIGS. 12A-12C are graphs showing duration, opening timing, and closing timing of an exhaust valve depending on an engine load and an engine speed in one form of the present disclosure.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

As those skilled in the art would realize, the described forms may be modified in various different ways, all without departing from the spirit or scope of the present disclosure.

Throughout this specification and the claims which follow, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

It is understood that the term “vehicle” or “vehicular” or other similar terms as used herein is inclusive of motor vehicles in general including hybrid vehicles, plug-in hybrid electric vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid electric vehicle is a vehicle that has two or more sources of power, for example a gasoline-powered and electric-powered vehicle.

Additionally, it is understood that some of the methods may be executed by at least one controller. The term controller refers to a hardware device that includes a memory and a processor configured to execute one or more steps that should be interpreted as its algorithmic structure. The memory is configured to store algorithmic steps, and the processor is specifically configured to execute said algorithmic steps to perform one or more processes which are described further below.

Furthermore, the control logic of the present disclosure may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, a controller, or the like. Examples of computer readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards, and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a controller area network (CAN).

FIG. 1 is a schematic block diagram showing a system for controlling valve timing of a continuous variable valve duration engine according to one form of the present disclosure.

An engine according one form of the present disclosure may be a turbo engine provided with a turbocharger.

As shown in FIG. 1, a system for controlling valve timing of a continuous variable valve duration engine includes: a data detector 100, a camshaft position sensor 120, a controller 300, an intake continuous variable valve duration (CVVD) device 400, an intake continuous variable valve timing (CVVT) device 450, an exhaust two-stage variable valve duration device 500, and an exhaust continuous variable valve timing (CVVT) device 550.

The data detector 100 detects data related to a running state of a vehicle for controlling the intake continuous variable valve duration (CVVD) device 400, the intake continuous variable valve timing (CVVT) device 450, the exhaust two-stage variable valve duration (VVD) device 500, and the exhaust continuous variable valve timing (CVVT) device 550. The data detector 100 includes: a vehicle speed sensor 111, an engine speed sensor 112, an oil temperature sensor 113, an air flow sensor 114, and an accelerator pedal position sensor (APS) 115, although other sensors may be employed.

The vehicle speed sensor 111 detects a vehicle speed, transmits a corresponding signal to the controller 300, and may be mounted at a wheel of the vehicle.

The engine speed sensor 112 detects a rotation speed of the engine from a change in phase of a crankshaft or camshaft, and transmits a corresponding signal to the controller 300.

The oil temperature sensor (OTS) 113 detects temperature of oil flowing through an oil control valve (OCV), and transmits a corresponding signal to the controller 300.

The oil temperature detected by the oil temperature sensor 113 may be determined by measuring a coolant temperature using a coolant temperature sensor mounted at a coolant passage of an intake manifold. Therefore, in one form, the oil temperature sensor 113 may include a coolant temperature sensor, and the oil temperature should be understood to include the coolant temperature.

The air flow sensor 114 detects an air amount drawn into the intake manifold, and transmits a corresponding signal to the controller 300.

The accelerator pedal position sensor (APS) 115 detects a degree in which a driver pushes an accelerator pedal, and transmits a corresponding signal to the controller 300. The position value of the accelerator pedal may be 100% when the accelerator pedal is pressed fully, and the position value of the accelerator pedal may be 0% when the accelerator pedal is not pressed at all.

A throttle valve position sensor (TPS) that is mounted on an intake passage may be used instead of the accelerator pedal position sensor 115. Therefore, in one form, the accelerator pedal position sensor 115 may include a throttle valve position sensor, and the position value of the accelerator pedal should be understood to include an opening value of the throttle valve.

The camshaft position sensor 120 detects a change of a camshaft angle, and transmits a corresponding signal to the controller 300.

FIG. 2 is a perspective view showing a continuous variable valve duration device and a continuous variable valve timing device which is disposed on an intake valve side, and a two-stage variable valve duration device and continuous variable valve timing device which is disposed on an exhaust valve side.

The intake continuous variable valve duration (CVVD) device 400 controls an opening duration of an intake valve of the engine according to a signal from the controller 300, the exhaust continuous variable valve duration (CVVD) device 500 controls an opening duration of an exhaust valve of the engine according to a signal from the controller 300.

FIG. 3 is a side view of the intake CVVD device in another form as assembled with the intake CVVT for intake valves 200 operating with cylinders 201, 202, 203, 204. In one form, two cams 71 and 72 may be formed on first and second cam portions 70 a and 70 b, and a cam cap engaging portion 76 may be formed between the cams 71 and 72 and supported by a cam cap 40. The valve 200 is opened and closed by being in contact with the cams 71 and 72.

As illustrated in FIG. 3, the intake CVVD device includes: a cam unit 70 in which a cam 71 is formed and into which a cam shaft 30 is inserted; an inner wheel 80 to transfer the rotation of the cam shaft 30 to the cam unit 70 (See, in FIG. 4); a wheel housing 90 in which the inner wheel 80 rotates and movable in a direction perpendicular to the camshaft 30; a guide shaft 132 having a guide thread and provided in a direction perpendicular to the camshaft 30, the guide shaft mounted by a guide bracket 134; a worm wheel 50 having an inner thread engaged with the guide thread and disposed inside the wheel housing 90; and a control shaft 102 formed with a control worm 104 meshing with the worm wheel 50. The control worm 104 is engaged with an outer thread formed on the outer side of the worm wheel 50. The intake CVVD device further includes a sliding shaft 135 fixed to the guide bracket 134 and guiding the movement of the wheel housing 90.

FIG. 4 is a partial view of the inner wheel 80 and the cam unit 70 of the intake CVVD device of the FIG. 3. Referring to FIG. 4, First and second sliding holes 86 and 88 are formed in the inner wheel 80, and a cam slot 74 is formed in the cam unit 70.

The intake CVVD device further includes: a roller wheel 60 inserted into the first sliding hole 86 allowing the roller wheel 60 to rotate; and a roller cam 82 inserted into the cam slot 74 and the the second sliding hole 88. The roller cam 82 may slide in the cam slot 74 and rotate in the second sliding hole 88.

The roller cam 82 includes: a roller cam body 82 a slidably inserted into the cam slot 74 and a roller cam head 82 b rotatably inserted into the second sliding hole 88.

The roller wheel 60 includes: a wheel body 62 slidably inserted into the camshaft 30 and a wheel head 64 rotatably inserted into the first sliding hole 86. A cam shaft hole 34 is formed in the camshaft 30 and a wheel body 62 of the roller wheel 60 is movably inserted into the camshaft hole 34.

FIGS. 5A-5C illustrate the operation of the intake CVVD device. FIG. 5A illustrates a neutral state in which the rotational center of the camshaft 30 and the cam unit 70 coincide with each other. In this case, the cams 71 and 72 rotate at the same speed as the camshaft 30. When the controller 300 applies a control signal based on engine load and/or engine speed, a control motor 106 rotates the control shaft 102. Then, the control worm 104 rotates the worm wheel 50 which in turn rotates and moves along the guide thread formed on the guide shaft 132.

As a result, the worm wheel 50 causes a change to a position of the wheel housing 90 relative to the cam shaft 30. As illustrated in FIGS. 5B and 5C, when the position of the wheel housing 90 moves in one direction with respect to the center of rotation of the camshaft 30, the rotational speed of the cams 71, 72 with respect to the camshaft 30 are changed in accordance with their phases. FIG. 7A and FIG. 8B are drawings showing a valve profile illustrating valve opening duration change by the operation of the intake CVVD device. The solid line represents a general valve profile (e.g., a current opening duration), and the dotted line shows the valve profile as a short opening duration (e.g., a target opening duration in FIG. 8B) is applied. FIG. 8A illustrates a changed valve profile when the long opening duration is applied by the CVVD device. The controller 300 determines a target opening duration based on an engine load and an engine speed and controls the intake CVVD device to modify current opening and closing timings of the intake valve based on the target opening duration.

More specifically, as illustrated in FIG. 8B, the intake CVVD device may retard the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve to shorten the opening duration according to a predetermined value provided by the controller 300. When the controller applies a longer opening duration (i.e., a target opening duration) than the current opening duration, as illustrated in FIG. 8A, the CVVD device may advance the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake vale so that the modified opening duration becomes longer than the current opening duration. FIGS. 8C and 8D illustrate the relationship between the operation of the CVVD device and the CVVT device. As discussed above, the CVVD device may change the opening duration of a valve (e.g., intake or exhaust valve) whereas the CVVT device may shift a valve profile according to a target opening and/or a target closing timings without change to the period of the valve opening duration. It should be noted that the changing opening duration by the CVVD device may occur after changing valve opening and/or closing timings of intake or exhaust valves by the CVVT device. In another form, the operation of the CVVT device to change the opening and closing timings may occur after the operation of the CVVD device. In still another form, the operation of the CVVD and CVVT devices may perform simultaneously to change the opening duration and the timing of opening and closing of intake or exhaust valves.

FIGS. 6A and 6B illustrate a view of the cam slot 74 a, 74 b of the intake CVVD device, and FIGS. 7A-7C illustrate valve profiles of the CVVD device in exemplary forms of the present disclosure.

Referring to FIGS. 6A-6B, the cam slot 74 a may be formed in an advanced position relative to the cam 71, 72, or in another form the cam slot 74 b may be formed in a retarded position relative to the cam 71, 72. In another form, the cam slot 74 a, 74 b may be formed to have the same phase as the lobe of the cam 71, 72. These variations are enable to realize various valve profiles. Based on the position of the cam slot 74 a, 74 b, and a contact position between the cam and the intake valve, the opening and closing timings of the intake valve may vary. FIG. 7B shows that the intake CVVD device may advance (for a short opening duration) or retard the current closing timing (for a long opening duration) of the intake valve by a predetermined value based on the target opening duration of the intake valve while maintaining the current opening timing of the intake valve. In another form, as illustrated in FIG. 7C, the intake CVVD device may advance (for a long opening duration) or retard (for a short opening duration) the current opening timing of the intake valve by a predetermined value based on the target opening duration of the intake valve while maintaining the current closing timing of the intake valve.

The exhaust two-stage variable valve duration (VVD; Variable Valve Duration) device 500 may control an opening duration of the exhaust valve of engine according to a signal from the controller 300 by switching the opening duration to two stages. That is, the exhaust two-stage VVD device 500 may use a solenoid valve without a motor and a sensor which is provided to an exhaust CVVD, thereby the manufacturing cost may be reduced. The structure and its operation of an two-stage VVD is similar to those of a two-stage variable valve lift (VVL) device except a profile of a cam of the two-stage VVL device. An exemplary form of the two-stage VVL device is disclosed in U.S. Pat. No. 7,328,675, which is incorporated herein by reference. More specifically, high/low lift cams of the two-stage VVL device can be replaced with high/low duration cams (i.e., short/long duration cams) to realize a two-stage VVD device.

When exhaust duration is longer, the fuel efficiency and a high-speed performance may be improved, however a low-speed performance may be deteriorated. Thereby, a short duration for the low-speed performance and a long duration for the high-speed performance should be set by experiment. For example the short duration may be approximately 180-210 degrees and the long duration may be approximately 240-250 degrees.

Thereby, the exhaust two-stage VVD device 500 may apply the short opening duration or long opening duration to the exhaust valve by switching.

The exhaust continuous variable valve timing (CVVT) device 550 controls opening and closing timings of the exhaust valve of the engine according to a signal from the controller 300.

The controller 300 may classify or determine a plurality of control regions depending on an engine speed and an engine load based on signals from the data detector 100 and camshaft position sensor 120, and control the intake CVVD and CVVT devices 400 and 450, and the exhaust two-stage VVD and CVVT devices 500 and 550 according to the control regions. Here, the plurality of control regions may be classified into six control regions.

The controller 300 applies a maximum duration (i.e., a target opening duration) to the intake valve and applies the long duration (i.e., a target opening duration) to the exhaust valve to limit a valve overlap in the first control region, applies the maximum duration to the intake and applies the long duration to the exhaust valves in order to control the control overlap according to the engine load in the second control region, applies the long duration to the exhaust valve and advances an intake valve closing (IVC) timing in the third control region, applies the short duration to the exhaust valve and controls the intake valve closing (IVC) timing close to a bottom dead center in the fourth control region, controls a wide open throttle valve (WOT) and applies the short duration to the exhaust valve to generate scavenging in the fifth control region, and controls a wide open throttle valve (WOT) and controls the intake valve closing (IVC) timing by applying the long duration to the exhaust valve to reduce knocking in the sixth control region.

For these purposes, the controller 300 may be implemented as at least one processor that is operated by a predetermined program, and the predetermined program may be programmed in order to perform each step of a method for controlling valve timing of a continuous variable valve duration engine according to the present disclosure.

Various forms described herein may be implemented within a recording medium that may be read by a computer or a similar device by using software, hardware, or a combination thereof, for example.

The hardware of the forms described herein may be implemented by using at least one of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, and electrical units designed to perform any other functions.

The software such as procedures and functions of the forms described in the present disclosure may be implemented by separate software modules. Each of the software modules may perform one or more functions and operations described in the present disclosure. A software code may be implemented by a software application written in an appropriate program language.

Hereinafter, a method for controlling valve timing of a continuous variable valve duration engine according to one form of the present disclosure will be described in detail with reference to FIG. 9A to FIG. 12C.

FIG. 9A and FIG. 9B are flowcharts showing a method for controlling valve timing of a continuous variable valve duration engine, and FIG. 10 is a schematic block diagram of showing control regions based on engine load (e.g., engine torque) and engine speed.

FIGS. 11A-11C are graphs showing duration, opening timing, and closing timing of an intake valve depending on an engine load and an engine speed, and FIGS. 12A-12C are graphs showing duration, opening timing, and closing timing of an exhaust valve depending on an engine load and an engine speed.

As shown in FIG. 9A and FIG. 9B, a method for controlling valve timing of a continuous variable valve duration engine starts with determining a plurality of control regions depending on an engine speed and an engine load by the controller 300 at step S100. The control region may be divided into six control regions (e.g., first, second, third, fourth, fifth and sixth control regions).

The control regions will be described with reference to FIG. 10, and FIGS. 11A-11C and FIGS. 12A-12C in more detail. The first to sixth control regions are indicated in the FIG. 4A to FIG. 5C. FIG. 10 schematically describes the control regions based on the engine load (e.g., engine torque) and engine speed (e.g., revolutions per minutes “rpm”). However, the control regions may vary based on an engine type or an engine size. Mixed control may be performed at the boundary of each region to minimize the control impact of the engine. Accordingly, the range of each region shown in the present application is exemplary, and the classification of each region may be varied.

The controller 300 may determine control regions as a first control region (namely, {circle around (1)} an idling region or a low-load condition) when the engine load is between a first predetermined load (e.g., a minimum engine torque) and a second predetermined load, a second control region (namely, {circle around (2)} an mid-load condition) when the engine load is greater than the second predetermined load and equal to or less than a third predetermined load, and a third control region (namely, {circle around (3)} a high-load condition) where the engine load is greater than the third predetermined load and less than a fourth predetermined load and the engine speed is between a first predetermined speed (e.g., an idle rpm) and a second predetermined speed, or where the engine load is greater than the third predetermined load and equal to or less than a fifth predetermined load and the engine speed is between the second predetermined speed and a third predetermined speed (i.e., an engine maximum rpm).

In addition, the controller 300 may determine a fourth control region (namely, {circle around (4)} a low-speed and high-load condition) when the engine load is greater than the fourth predetermined load and equal to or less than a fifth predetermined load and the engine speed is equal to or greater than the first predetermined speed and equal to or less than the second predetermined speed, a fifth control region (namely, {circle around (5)} a low speed-wide open throttle “WOT” condition) when the engine load is greater than the fifth predetermined load and equal to or less than a maximum engine load and the engine speed is between the first and second predetermined speeds, and a sixth control region (namely, {circle around (6)} an mid-high speed-WOT condition) when the engine load is greater than the fifth predetermined load and equal to or less than the maximum engine load and the engine speed is greater than the second predetermined speed and equal to or less than a third predetermined speed (e.g., an engine maximum rpm).

Referring to FIG. 10, the first predetermined load (e.g., a minimum engine torque) is measured when a input from the APS is zero “0,” and the second to fifth predetermined loads, and the second and third predetermined engine speeds may be calculated by the following equations:

Second predetermined load=min_L+(1/5)×(max_L−min_L);

Third predetermined load=min_L+(2/5)×(max_L−min_L);

Fourth predetermine load=min_L+(1/2)×(max_L−min_L);

Fifth predetermined load=min_L+(4/5)×(max_L−min_L);

Second predetermined engine speed=min_S+(3/10)×(max_S-min_S); and

Third predetermined engine speed=max_S,

-   -   where, min_L is the minimum engine torque; max_L is a maximum         engine torque; min_S is a minimum engine rpm (e.g., Idle rpm);         and max_S is a maximum engine rpm.

Meanwhile, referring to FIGS. 11A-11C and FIGS. 12A-12C, a crank angle is marked in an intake valve duration (IVD) map and an exhaust valve duration (EVD) map, which indicating the opening time of the intake valve and exhaust valve. For example, regarding the IVD map in FIG. 11A, a curved line written as a number 200 at inner side of the fourth region means that the crank angle is approximately 200 degrees, a curved lined marked as a number 220 at outer side of the number 200 means that the crank angle is approximately 220 degrees. Although not shown in the drawing, the crank angle which is approximately more than approximately 200 degrees and less than approximately 220 degrees is positioned between the curved line of the number 200 and the curved line of the number 220.

In addition, a unit of number designated in an intake valve opening (IVO) timing map is before a top dead center (TDC), a unit of number designated in an intake valve closing (IVC) timing map is after a bottom dead center (BDC), a unit of number designated in an exhaust valve opening (EVO) timing map is before BDC, and a unit of number designated in an exhaust valve closing (EVC) map is after TDC.

Each region and curved line in FIG. 11A to FIG. 12C are one form of the present disclosure, it may be modified within the technical idea and scope of the present disclosure.

Referring to FIGS. 9A to 12C, the control regions are determined according to the engine speed and load in the step of S100. After that, the controller 300 determines whether the engine state is under the first control region at step S110.

In the step of S110, if the engine load is between first and second predetermined loads, the controller 300 determines that the engine state is under the first control region. At this time, the controller 300 applies a maximum duration, or a first intake opening duration to the intake valve and applies the long duration (i.e., a target opening duration) to the exhaust valve to control a valve overlap between the exhaust valve and intake valve at step S120. The valve overlap is a state where the intake valve is opened and the exhaust valve is not closed yet.

In other words, when the engine is under low load, then the controller 300 may control both the intake valve opening (IVO) timing and the intake valve closing (IVC) timing being fixed such that the intake valve has a maximum duration value. In one form, the controller 300 may control the intake CVVD device to adjust a current opening duration to the first intake opening duration by advancing the IVO timing and retarding the IVC. As shown in FIGS. 11A-11C, the first control region may be approximately 0 to 10 degrees before TDC in the IVO timing map and approximately 100 to 110 degrees after BDC in the IVC timing map.

Also, the controller 300 may control the EVO timing to be fixed and set up the EVC timing. Meanwhile, as the valve overlap is increased, the fuel consumption is cut, whereas the combustion stability is deteriorated. Accordingly, properly setting the valve overlap is desired. However, according to the present disclosure, it is possible to get highly improved fuel-efficiency by setting desired valve overlap up, which fixing the EVO timing and controlling the EVC timing to be set up at a maximum value within sustainable combustion stability. The timing value may be determined by a predetermined map.

For example, as shown in FIGS. 12A-12C, the EVO timing may be fixed at approximately 40 to 50 degrees before BDC, the EVC timing may be established by moving the degrees thereof in an after TDC direction. The EVC timing may be a maximum value such that the combustion stability is sustainable.

When the current engine state does not belong to the first control region at the step S110, the controller 300 may determine whether the current engine state belongs to the second control region at step S130. However, each of the control regions may be determined immediately by the controller 300 based on the engine load and/or engine speed.

In the step of S130, if the engine load is greater than the second predetermined load and equal to or less than the third predetermined load, the controller 300 determines that the engine state is under the second control region. At this time, controller 300 applies the maximum duration to the intake valve and applies the long duration to the exhaust valve in order to control the control overlap according to the engine load at step S140.

The controller 300 may control EVC timing to be late in a direction after a top dead center as the engine load reaches a predetermined load, thereby the control overlap may be increased.

Herein, the intake pumping is decreased as the EVC timing is controlled to be late in a direction after the top dead center, however the exhaust pumping is increased as the EVO timing approaches to the bottom dead center. Therefore, the controller 300 controls the increased control overlap to be shorten by advancing the EVC timing to the locking position when the engine load is increased more than the predetermined load.

In addition, the controller 300 may control the IVC timing at the LIVC position (Late Intake Valve Closing; an angle of approximately 100-110 degrees after BDC) by applying a maximum duration to the intake valve in order to inhibit or prevent from the knocking as the engine load is increased

When the current engine state does not belong to the second control region at the step S130, the controller 300 determines whether the current engine state belongs to the third control region at step S150.

In the step of S150, if the engine load is greater than the third predetermined load and less than a fourth predetermined load and the engine speed is between first and second predetermined speeds, or when the engine load is greater than the third predetermined load and equal to or less than a fifth predetermined load and the engine speed is between the second predetermined speed and a third predetermined speed, the controller 300 determines that the engine state is under the third control region. At this time, controller 300 applies the long duration to the exhaust valve and advances an intake valve closing (IVC) timing at step S160.

The IVC timing is controlled at the LIVC position (Late Intake Valve Closing; an angle of approximately 100-110 degrees after BDC, referring to FIGS. 11A-11C) in the first and second control regions. By the way, since the IVC timing is retarded at the LIVC position, the average pressure in the intake manifold (boost pressure) may be increased and the knocking is generated as the engine load is increased. Accordingly, the fuel efficiency may be deteriorated. Therefore, the controller 300 advances the IVC timing to inhibit or prevent effect as described above in the third control region which has relatively higher load.

At this time, the controller 300 may rapidly advance the IVC timing close to BDC when the engine speed is less than the predetermined speed so as to reflect characteristic of the turbo engine, as shown in FIGS. 11A-11C. In addition, if the engine speed is greater or equal to the predetermined speed, the controller 300 may slowly advance the IVC timing at an angle of approximately 30-50 degrees after BDC because the boost pressure is relatively lower. The predetermined speed may be approximately 1500 rpm.

As shown in FIGS. 12A-12C, the long duration is applied to the exhaust valve of both the second control region and the third control region. The long duration of exhaust valve may be set at approximately 240-250 so as to decrease exhaust pumping and increase the control overlap.

When the current engine state does not belong to the third control region at the step S150, the controller 300 determines whether the current engine state belongs to the fourth control region at step S170. In another form, the controller 300 may determine the condition for the fourth control region without performing the step of determining the first, second and third control regions.

If the engine state is under the fourth control region in the S170, the controller 300 applies the short duration to the exhaust valve and controls the intake valve closing (IVC) timing close to the bottom dead center at step S180.

The fourth control region may be a low boost region (or, a low-speed and high-load region) that the engine load is greater than the fourth predetermined load and equal to or less than the fifth predetermined load and the engine speed is greater than or equal to the first predetermined speed and less than the second predetermined speed. For example, the first predetermined speed (i.e., an idle rpm) may be approximately 1500 rpm or less, and the second predetermined speed may be approximately 2500 rpm.

The controller 300 controls the IVC timing close to BDC due to improving fuel efficiency in the fourth region, which is in the low boost region. In addition, the controller 300 may shorten the valve overlap between the intake valve and the exhaust valve and improve the combustion stability by approaching the IVO timing and EVC timing close to the TDC. For this purpose, controller 300 may apply the short duration to the exhaust valve instead of the long duration.

Resultantly, the short duration (e.g., approximately 180 degrees) may be applied to the intake and exhaust valve in the fourth control region.

When the current engine state does not belong to the fourth control region at the step S170, the controller 300 determines whether the current engine state belongs to the fifth control region at step S190.

In the S190, if the engine load is greater than the fifth predetermined load and equal to or less than a maximum engine load and the engine speed is between the first and second predetermined speeds, then the controller 300 determines that the engine state is under the fifth control region. At this time, controller 300 controls a wide open throttle valve (WOT) and applies the short duration to the exhaust valve to generate scavenging at step S200. More specifically, the fresh air at a higher pressure than that of the burned gases (combustion gas) scavenges the burned gases and evacuates them through the exhaust valve, thus filling the space freed by these gases.

In the turbo engine, if the throttle valve is controlled to be wide open (WOT) when the engine speed is less than the predetermined speed (e.g., 1500 rpm), intake port pressure becomes higher than exhaust port pressure by boosting. Therefore, an effect of a scavenging phenomenon which emits combustion gas of the exhaust is prominent in the turbo engine compared to a natural aspirated engine.

Accordingly, as shown in FIGS. 11A-11C, the controller 300 may advance the IVO timing at an angle of approximately 20-40 degrees before BDC to generate the scavenging, and control the IVC timing at angle of approximately 0-20 degrees after BDC.

Moreover, as shown in FIGS. 12A-12C, the controller 300 may sufficiently retard the EVO timing to after BDC so as to maximally generate the scavenging by reducing interference of exhaust. Furthermore, the EVC timing may be controlled within an angle of approximately 30 degrees after TDC in order to maintain catalyst temperature. Accordingly, the short duration is applied to the exhaust valve in the fifth control region.

When the current engine state does not belong to the fifth control region at the step S190, the controller 300 determines whether the current engine state belongs to the sixth control region at step S210.

In the step of S210, if the engine load is greater than the fifth predetermined load and equal to or less than the maximum engine load, and the engine speed is greater than the second predetermined speed (e.g., approximately 2500 rpm) and less than a third predetermined speed (e.g., a maximum rpm of an engine), then the controller determines the engine state is under the sixth control region. At this time, controller 300 controls a wide open throttle valve (WOT), controls the intake valve closing (IVC) timing by applying the long duration to the exhaust valve so as to reduce exhaust pumping and knocking by lowering the boost pressure at step S220.

When the engine speed is greater than a predetermined speed (e.g., approximately 3500 rpm) in the sixth control region, the scavenging phenomenon disappears because exhaust port pressure is much higher than intake port pressure. Therefore, as shown in FIGS. 12A-12C, the controller 300 advances the EVO timing an angle of approximately 30 degrees before BDC and approaches the EVC timing close to the TDC to inhibit or prevent an exhaust pumping. At this time, the controller 300 may apply the long duration to the exhaust valve instead of the short duration which is used in the fifth control region by switching.

Meanwhile, when WOT control is performed at a high speed condition, knocking is rarely generated in the natural aspirated engine, on the contrary, knocking may be deteriorated in the turbo engine. Thus, as shown in FIGS. 11A-11C, the controller 300 may advance the IVC timing within an angle of approximately 50 degrees after BDC to reduce knocking by decreasing boost pressure.

As described above, duration and timing of the continuous variable valve are simultaneously controlled, so the engine may be controlled under desired conditions.

That is, since opening timing and closing timing of the intake valve and the exhaust valve are appropriately controlled, the fuel efficiency under a partial load condition and engine performance under a high load condition are improved. In addition, a starting fuel amount may be reduced by increasing a valid compression ratio, and exhaust gas may be reduced by shortening time for heating a catalyst.

In addition, the cost reduction and power performance may be realized by providing the two-stage VVD device to the exhaust valve side.

While this present disclosure has been described in connection with what is presently considered to be practical exemplary forms, it is to be understood that the present disclosure is not limited to the disclosed forms. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for controlling intake and exhaust valves of an engine, the method comprising: controlling, by an intake continuous variable valve timing (CVVT) device, opening and closing timings of the intake valve; controlling, by an exhaust CVVT device, opening and closing timing of the exhaust valve; determining, by a controller, a target opening duration of the intake valve, a target opening duration of the exhaust valve, and at least one of a target opening timing or a target closing timing of the intake valve and the exhaust valve, based on an engine load and an engine speed; modifying, by an intake continuous variable valve duration (CVVD) device, current opening and closing timings of the intake valve based on the target opening duration of the intake valve; modifying, by an exhaust two-stage variable valve duration (VVD) device, current opening and closing timings of the exhaust valve based on the target opening duration of the exhaust valve; advancing, by the intake CVVD device, the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve by a predetermined value, or retarding the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve by a predetermined value, based on the target opening duration of the intake valve; and switching, by the exhaust two-stage VVD device, a current opening duration of the exhaust valve to a first exhaust opening duration or a second exhaust opening duration which is shorter than the first opening duration, based on the target opening duration of the exhaust valve.
 2. The method of claim 1, wherein the intake CVVD device advances the current opening timing of the intake valve while simultaneously retarding the current closing timing of the intake valve when the target opening duration of the intake valve is longer than a duration between the current opening timing and current closing timing of the intake valve.
 3. The method of claim 1, wherein the intake CVVD device retards the current opening timing of the intake valve while simultaneously advancing the current closing timing of the intake valve when the target opening duration of the intake valve is shorter than a duration between the current opening timing and current closing timing of the intake valve.
 4. The method of claim 1, further comprising the step of adjusting, by the intake CVVT device, the current opening and closing timings of the intake valve to the target opening and closing timings of the intake valve, respectively.
 5. The method of claim 1, further comprising the step of adjusting, by the exhaust CVVT device, the current opening and closing timings of the exhaust valve to the target opening and closing timings of the exhaust valve, respectively.
 6. The method of claim 1, wherein, during the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to a first intake opening duration in a first control region where the engine load is between first and second predetermined loads, and the controller controls the intake CVVD device to adjust a current intake opening duration to the first intake opening duration, and wherein the exhaust two-stage VVD device applies the first exhaust opening duration to the exhaust valve so as to control a valve overlap between the exhaust valve and the intake valve in the first control region.
 7. The method of claim 6, further comprising the step of fixing the opening and closing timings of the intake valve and the opening timing of the exhaust valve, and setting up the closing timing of the exhaust valve at a maximum value within sustainable combustion stability in the first control region.
 8. The method of claim 6, wherein, during the step of determining the target opening duration of the intake valve, the controller sets the target opening duration of the intake valve to the first intake opening duration in a second control region where the engine load is greater than the second predetermined load and equal to or less than a third predetermined load, and the controller controls the intake CVVD device to adjust a current intake opening duration to the first intake opening duration and the exhaust two-stage VVD device to apply the first exhaust opening duration to the exhaust valve.
 9. The method of claim 8, wherein the exhaust CVVT device retards the closing timing of the exhaust valve as the engine load is increased so as to increase the valve overlap, and after when the engine load is greater than or equal to a predetermined load, the exhaust CVVT device advances the closing timing of the exhaust valve to decrease the valve overlap in the second control region.
 10. The method of claim 1, further comprising the step of determining, by the controller, a third control region where the engine load is greater than a third predetermined load and less than a fourth predetermined load and the engine speed is between first and second predetermined speeds, or where the engine load is greater than the third predetermined load and equal to or less than a fifth predetermined load and the engine speed is between the second predetermined speed and a third predetermined speed; and applying, by the two-stage VVD device, the first exhaust opening duration to the exhaust valve, and advancing, by the intake CVVT device, the closing timing of the intake valve in the third control region.
 11. The method of claim 10, wherein, in the third control region, the intake CVVT device advances the closing timing of the intake valve to be approximately at a bottom dead center when the engine speed is less than a predetermined speed, the intake CVVT device advances the closing timing of the intake valve to an angle after the bottom dead center when the engine speed is greater than or equal to the predetermined speed.
 12. The method of claim 1, further comprising the step of determining a fourth control region, by the controller, where the engine load is greater than a fourth predetermined load and equal to or less than a fifth predetermined load and the engine speed is equal to or greater than a first predetermined speed and equal to or less than a second predetermined speed; and applying, by the two-stage VVD device, the second exhaust opening duration to the exhaust valve, and controlling, by the intake CVVT device, the closing timing of the intake valve to be approximately at a bottom dead center in the fourth control region.
 13. The method of claim 12, wherein, in the fourth control region, the controller controls the opening timing of the intake valve via the intake CVVT device and the closing timing of the exhaust valve to approach at a top dead center so as to reduce a valve overlap.
 14. The method of claim 1, further comprising the step of determining, by the controller, a fifth control region where the engine load is greater than a fifth predetermined load and equal to or less than a maximum engine load and the engine speed is between first and second predetermined speeds, and controlling, by the controller, a wide open throttle valve (WOT) and applying the second exhaust opening duration to the exhaust valve in the fifth control region such that an fresh air introduced into a cylinder evacuates a combustion gas from the cylinder.
 15. The method of claim 14, wherein, in the fifth control region, the intake CVVT device advances the opening timing of the intake valve to be before a top dead center to generate the scavenging and controls the closing timing of the intake valve to be after the bottom dead center.
 16. The method of claim 15, wherein, in the fifth control region, the controller retards the opening timing of the exhaust valve to be after a bottom dead center so as to reduce interference of exhaust and controls the closing timing of the exhaust valve to be after a top dead center to maintain a catalyst temperature.
 17. The method of claim 1, further comprising the step of determining, by the controller, a sixth control region where the engine load is greater than a fifth predetermined load and equal to or less than a maximum engine load and the engine speed is greater than a second predetermined speed and equal to or less than a third predetermined speed; and controlling a wide open throttle valve (WOT) by the controller, controlling the closing timing of the intake valve by the intake CVVT device, and applying the first exhaust opening duration to the exhaust valve by the two-stage VVD device, in the sixth control region, so as to reduce a knocking in the sixth control region.
 18. The method of claim 17, wherein, in the sixth control region, the controller advances the opening timing of the exhaust valve to be before a bottom dead center to inhibit an exhaust pumping and to lower boost pressure, and the controller controls the closing timing of the exhaust valve to be approximately at a top dead center. 